This randomized study investigates whether feeding very low birth weight (VLBW) infants with mother’s own milk (MOM) supplemented with either preterm (PDM) or term donor milk (TDM), when MOM is insufficient, has a positive impact on infants’ protein intake and growth. A hundred and twenty VLBW infants were randomized into two groups. Group A (43 infants) received MOM supplemented with PDM, whereas Group B (77 infants) was fed with MOM supplemented with TDM, for the first three weeks of life (donor milk period). Breast milk fortifier was added when milk feeds exceeded 50 mL/Kg/day. After the donor milk period, both groups were fed with formula when MOM was not available or the milk bank was unable to provide TDM. Protein intake was higher in Group A than in Group B at initiation of milk fortification (p = 0.006), as well as during the 3-week donor milk period (p = 0.023) and throughout hospitalization (p = 0.014). Moreover, Group A presented higher Δz-score for body weight (p = 0.019) and head circumference (p = 0.001) from birth to the end of donor milk period, and higher mean body weight at discharge (p = 0.047) compared to Group B. In conclusion, when donor milk is required, PDM positively impacts protein intake and growth in VLBW infants (NCT05675397).